1. Technical Field
The present invention relates to a piezoelectric driving device for a motor, a motor, a robot, and a pump.
2. Related Art
Piezoelectric actuators (piezoelectric driving devices for a motor) which vibrate a piezoelectric body to drive a driven body, do not need a magnet or a coil, and accordingly, are used in various fields.
Japanese Patent No. 2847758, for example, discloses an ultrasonic motor (piezoelectric driving device for a motor) which rotates a rotor disposed to come into contact with an elastic plate by using resonance vibration in a primary longitudinal vibration mode in a longitudinal direction of the elastic plate including one fixed edge and the other free edge, and resonance vibration in a higher bending vibration mode in a longitudinal direction. In such a piezoelectric driving device, it is possible to efficiently rotate a rotor by decreasing a difference between a resonance frequency in longitudinal vibration and a resonance frequency in bending vibration (transverse vibration).
JP-A-2004-140947, for example, discloses a driving device including a vibrating plate including a piezoelectric element, an arm portion supporting the vibrating plate, and a fixed plate vibratably supporting the vibrating plate via the arm portion, in which the arm portion supports the approximate center of the vibrating plate in a longitudinal direction at two supporting points from both sides.
However, in the piezoelectric driving device disclosed in Japanese Patent No. 2847758, a rotor is disposed so as to come into contact with a main surface of a vibrating plate (an upper surface of a vibrating plate). Accordingly, in the piezoelectric driving device disclosed in Japanese Patent No. 2847758, since the vibrating plate is pressed in a vertical direction of the main surface of the vibrating plate, the vibrating plate may be damaged due to concentration of stress on a boundary between a fixed portion (portion interposed by a jig of the vibrating plate) and a vibrating portion of the vibrating plate. Thus, a force for pressing the vibrating plate is hardly increased and output may not be increased.
In addition, in the piezoelectric driving device disclosed in JP-A-2004-140947, the arm portion supporting the vibrating plate is a thin and long member so as not to disturb vibration of the vibrating plate, and the arm portion may be damaged due to stress (shear stress) applied to such a thin and long member, for example. Thus, a force for pressing the vibrating plate is hardly increased and output may not be increased.